Regulation of motor proteins, axonal transport deficits and adult-onset neurodegenerative diseases

© The Author(s), 2017. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Neurobiology of Disease 105 (2017): 273-282, doi:10.1016/j.nbd.2017.04.010.Neurons affected in a wide variety of unrelated adult-onset neurodegenerative diseases (AONDs) typically exhibit a “dying back” pattern of degeneration, which is characterized by early deficits in synaptic function and neuritic pathology long before neuronal cell death. Consistent with this observation, multiple unrelated AONDs including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and several motor neuron diseases feature early alterations in kinase-based signaling pathways associated with deficits in axonal transport (AT), a complex cellular process involving multiple intracellular trafficking events powered by microtubule-based motor proteins. These pathogenic events have important therapeutic implications, suggesting that a focus on preservation of neuronal connections may be more effective to treat AONDs than addressing neuronal cell death. While the molecular mechanisms underlying AT abnormalities in AONDs are still being analyzed, evidence has accumulated linking those to a well-established pathological hallmark of multiple AONDs: altered patterns of neuronal protein phosphorylation. Here, we present a short overview on the biochemical heterogeneity of major motor proteins for AT, their regulation by protein kinases, and evidence revealing cell type-specific AT specializations. When considered together, these findings may help explain how independent pathogenic pathways can affect AT differentially in the context of each AOND.The authors would like to acknowledge funding from CHDI and NIH grants RO1 NS066942A, R21 NS096642 (to G.M) and R01-NS023868 and R01-NS041170 and a Zenith Award from the Alzheimer’s Association (to STB).2018-04-1

Lightweight means of actuation for use in space-based robotics applications

In the field of robotics many researchers have devoted a large amount of time to pursuing means to reduce the weight of robotic systems. For space robotics, this becomes even more important due to launch cost being directly affected by weight. During review, potential progress involving weight reduction of actuators has been encountered, which it is necessary to investigate further in order to ascertain the potential advantages and disadvantages of such work. The contribution to be put forth here is a review of means by which reductions in weight can be achieved, with particular emphasis on space robotic actuation sub-systems. Ideas will be posited about the possible configurations which could be explored to reduce weight whilst attempting to maintain performance. It is expected that this contribution will provide evidence-based support for some future research directions, and will also help to stimulate discussion and further work on the subject of lightweight robotics and lightweight actuators. The next stages of this project aim to enhance some of the actuation ideas investigated so far, test these comparatively against one another, and critically review them alongside existing lightweight actuation methods. Following this, simulation of actuation concepts being applied to robotic applications will take place. This is in order to evaluate their performance in microgravity environments and to test their versatility. This process, as part of this project, will also be discussed in this pape

Laboratory Notes From Behavioral Pharmacologists and Trainees: Considerations for the Discipline

In several laboratory meetings, we discussed the challenges that face trainees in behavioral pharmacology. Major concerns, such as a difficult funding climate and limited academic job prospects were discussed at first. However, we decided to concentrate on ways to meet these challenges; versus focusing on negatives and listing gripes. Within this more constructive framework, we identified the importance of broadening training to aligned areas to enhance the capacity of behavioral pharmacologists to collaborate in multidisciplinary teams. With increased breadth of training comes the concern for a balance that does not cheat trainees out of the depth of training also needed for success. We believe that behavioral pharmacologists trained in this manner will be ideally positioned to be leaders of these translational research teams. Related to the breadth and depth of training is the recent concerns over replicability and reproducibility of published research. Behavioral pharmacologists, with the rigors of training in behavioral analysis and experimental design, can be at the forefront of this conversation. This will be especially true if current training is reinforced with additional experience in the use of cutting-edge statistical tools that address the complex experimental designs and large data sets that emerge from modern multidisciplinary collaborations. Finally, communicating the import and potential societal impact of our research to legislators, other scientists, educators, school children, neighbors, and acquaintances is needed to ensure that our field thrives. In closing, the process of explicitly discussing the challenges and potential solutions with current trainees will enhance their mentoring and training

Laboratory Notes From Behavioral Pharmacologists and Trainees: Considerations for the Discipline

In several laboratory meetings, we discussed the challenges that face trainees in behavioral pharmacology. Major concerns, such as a difficult funding climate and limited academic job prospects were discussed at first. However, we decided to concentrate on ways to meet these challenges; versus focusing on negatives and listing gripes. Within this more constructive framework, we identified the importance of broadening training to aligned areas to enhance the capacity of behavioral pharmacologists to collaborate in multidisciplinary teams. With increased breadth of training comes the concern for a balance that does not cheat trainees out of the depth of training also needed for success. We believe that behavioral pharmacologists trained in this manner will be ideally positioned to be leaders of these translational research teams. Related to the breadth and depth of training is the recent concerns over replicability and reproducibility of published research. Behavioral pharmacologists, with the rigors of training in behavioral analysis and experimental design, can be at the forefront of this conversation. This will be especially true if current training is reinforced with additional experience in the use of cutting-edge statistical tools that address the complex experimental designs and large data sets that emerge from modern multidisciplinary collaborations. Finally, communicating the import and potential societal impact of our research to legislators, other scientists, educators, school children, neighbors, and acquaintances is needed to ensure that our field thrives. In closing, the process of explicitly discussing the challenges and potential solutions with current trainees will enhance their mentoring and training

An engineering design tool capable of nurturing the development of new mechatronic actuators

This paper will cover use of a component selection tool in understanding and forecasting the actuation needs of robotic systems in the future. As part of an ongoing work, a component selection tool to assist mechatronics engineers has been developed. Pursuant to the conference's theme, this paper will focus on how effective the tool is in nurturing innovation of new actuation components and systems. Discussion will take place covering topics such as: development and intended primary and secondary applications of the component selection tool; applying the tool to component selection; how the tool can be used to identify ideal requirements in a design process; how the tool can be used to generate solutions which attempt to encompass what is required of an ideal solution; how the tool is relevant to mechatronics presently; and, how ongoing use could affect a paradigmatic shift in the field of mechatronic systems design and configuration

Pseudophosphorylation of tau at S422 enhances SDS-stable dimer formation and impairs both anterograde and retrograde fast axonal transport

AbstractIn Alzheimer's disease (AD), tau undergoes numerous modifications, including increased phosphorylation at serine-422 (pS422). In the human brain, pS422 tau protein is found in prodromal AD, correlates well with cognitive decline and neuropil thread pathology, and appears associated with increased oligomer formation and exposure of the N-terminal phosphatase-activating domain (PAD). However, whether S422 phosphorylation contributes to toxic mechanisms associated with disease-related forms of tau remains unknown. Here, we report that S422-pseudophosphorylated tau (S422E) lengthens the nucleation phase of aggregation without altering the extent of aggregation or the types of aggregates formed. When compared to unmodified tau aggregates, the S422E modification significantly increased the amount of SDS-stable tau dimers, despite similar levels of immunoreactivity with an oligomer-selective antibody (TOC1) and another antibody that reports PAD exposure (TNT1). Vesicle motility assays in isolated squid axoplasm further revealed that S422E tau monomers inhibited anterograde, kinesin-1 dependent fast axonal transport (FAT). Unexpectedly, and unlike unmodified tau aggregates, which selectively inhibit anterograde FAT, aggregates composed of S422E tau were found to inhibit both anterograde and retrograde FAT. Highlighting the relevance of these findings to human disease, pS422 tau was found to colocalize with tau oligomers and with a fraction of tau showing increased PAD exposure in the human AD brain. This study identifies novel effects of pS422 on tau biochemical properties, including prolonged nucleation and enhanced dimer formation, which correlate with a distinct inhibitory effect on FAT. Taken together, these findings identify a novel mechanistic basis by which pS422 confers upon tau a toxic effect that may directly contribute to axonal dysfunction in AD and other tauopathies

Analysis of isoform-specific tau aggregates suggests a common toxic mechanism involving similar pathological conformations and axonal transport inhibition

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Neurobiology of Aging 47 (2016): 113–126, doi:10.1016/j.neurobiolaging.2016.07.015.Misfolded tau proteins are characteristic of tauopathies, but the isoform composition of tau inclusions varies by tauopathy. Using aggregates of the longest tau isoform (containing 4 microtubule-binding repeats and 4-repeat tau), we recently described a direct mechanism of toxicity that involves exposure of the N-terminal phosphatase-activating domain (PAD) in tau, which triggers a signaling pathway that disrupts axonal transport. However, the impact of aggregation on PAD exposure for other tau isoforms was unexplored. Here, results from immunochemical assays indicate that aggregation-induced increases in PAD exposure and oligomerization are common features among all tau isoforms. The extent of PAD exposure and oligomerization was larger for tau aggregates composed of 4-repeat isoforms compared with those made of 3-repeat isoforms. Most important, aggregates of all isoforms exhibited enough PAD exposure to significantly impair axonal transport in the squid axoplasm. We also show that PAD exposure and oligomerization represent common pathological characteristics in multiple tauopathies. Collectively, these results suggest a mechanism of toxicity common to each tau isoform that likely contributes to degeneration in different tauopathies.This work was supported by NIH grants R01 AG044372 (Nicholas M. Kanaan), R01 NS082730 (Nicholas M. Kanaan and Scott T. Brady), BrightFocus Foundation (A2013364S, Nicholas M. Kanaan), the Jean P. Schultz Biomedical Research Endowment (Nicholas M. Kanaan), the Secchia Family Foundation (Nicholas M. Kanaan) and NS066942A (Gerardo Morfini)

Tau: a signaling hub protein

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Mueller, R. L., Combs, B., Alhadidy, M. M., Brady, S. T., Morfini, G. A., & Kanaan, N. M. Tau: a signaling hub protein. Frontiers in Molecular Neuroscience, 14, (2021): 647054, https://doi.org/10.3389/fnmol.2021.647054.Over four decades ago, in vitro experiments showed that tau protein interacts with and stabilizes microtubules in a phosphorylation-dependent manner. This observation fueled the widespread hypotheses that these properties extend to living neurons and that reduced stability of microtubules represents a major disease-driving event induced by pathological forms of tau in Alzheimer’s disease and other tauopathies. Accordingly, most research efforts to date have addressed this protein as a substrate, focusing on evaluating how specific mutations, phosphorylation, and other post-translational modifications impact its microtubule-binding and stabilizing properties. In contrast, fewer efforts were made to illuminate potential mechanisms linking physiological and disease-related forms of tau to the normal and pathological regulation of kinases and phosphatases. Here, we discuss published work indicating that, through interactions with various kinases and phosphatases, tau may normally act as a scaffolding protein to regulate phosphorylation-based signaling pathways. Expanding on this concept, we also review experimental evidence linking disease-related tau species to the misregulation of these pathways. Collectively, the available evidence supports the participation of tau in multiple cellular processes sustaining neuronal and glial function through various mechanisms involving the scaffolding and regulation of selected kinases and phosphatases at discrete subcellular compartments. The notion that the repertoire of tau functions includes a role as a signaling hub should widen our interpretation of experimental results and increase our understanding of tau biology in normal and disease conditions.This work was supported by NIH grants (R01AG067762 and R01AG044372 to NK, R01NS082730 to NK and SB, R01NS118177 and R21NS120126 to GM, R01NS023868 and R01NS041170 to SB), a gift from Neurodegenerative Research Inc. (GM), a Zenith Award from the Alzheimer’s Association (SB), a grant from the Secchia Family Foundation (NK), NIH/National Institute on Aging (NIA) funded Michigan Alzheimer’s Disease Research Center 5P30AG053760 (BC), the Office of the Assistant Secretary of Defense for Health Affairs through the Peer-Reviewed Alzheimer’s Research Program (Award No. W81XWH-20-1-0174 to BC), and an Alzheimer’s Association Research Grant 20-682085 (BC)

Defined tau phosphospecies differentially inhibit fast axonal transport through activation of two independent signaling pathways

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Morris, S. L., Tsai, M., Aloe, S., Bechberger, K., Konig, S., Morfini, G., & Brady, S. T. Defined tau phosphospecies differentially inhibit fast axonal transport through activation of two independent signaling pathways. Frontiers in Molecular Neuroscience, 13, (2021): 610037, https://doi.org/10.3389/fnmol.2020.610037.Tau protein is subject to phosphorylation by multiple kinases at more than 80 different sites. Some of these sites are associated with tau pathology and neurodegeneration, but other sites are modified in normal tau as well as in pathological tau. Although phosphorylation of tau at residues in the microtubule-binding repeats is thought to reduce tau association with microtubules, the functional consequences of other sites are poorly understood. The AT8 antibody recognizes a complex phosphoepitope site on tau that is detectable in a healthy brain but significantly increased in Alzheimer’s disease (AD) and other tauopathies. Previous studies showed that phosphorylation of tau at the AT8 site leads to exposure of an N-terminal sequence that promotes activation of a protein phosphatase 1 (PP1)/glycogen synthase 3 (GSK3) signaling pathway, which inhibits kinesin-1-based anterograde fast axonal transport (FAT). This finding suggests that phosphorylation may control tau conformation and function. However, the AT8 includes three distinct phosphorylated amino acids that may be differentially phosphorylated in normal and disease conditions. To evaluate the effects of specific phosphorylation sites in the AT8 epitope, recombinant, pseudophosphorylated tau proteins were perfused into the isolated squid axoplasm preparation to determine their effects on axonal signaling pathways and FAT. Results from these studies suggest a mechanism where specific phosphorylation events differentially impact tau conformation, promoting activation of independent signaling pathways that differentially affect FAT. Implications of findings here to our understanding of tau function in health and disease conditions are discussed.This research was funded by NIH grants R21NS096642 (GM); 1R01NS118177-01A1 (GM), R01 NS082730 (SB), a Zenith Award from the Alzheimer’s Association (SB), and a grant from the Tau Consortium/Rainwater Foundation (SB)

The Importance of Acquisition Learning on Nicotine and Varenicline Drug Substitution in a Drug-Discriminated Goal-Tracking Task

Nicotine and varenicline (Chantix®; the leading non-nicotine cessation pharmacotherapy) can come to control appetitive behaviors such as goal-tracking. We tested rats (N = 48) in a drug-discriminated goal-tracking (DGT) task where each rat received daily subcutaneous injections of either nicotine (0.4 mg/kg) or saline (0.9% [w/v]) interspersed across the acquisition phase (Phase 1). On saline days, sucrose was intermittently available. On nicotine days, sucrose was withheld. All rats acquired the discrimination with increased goal-tracking rates on saline days relative to nicotine days. Following acquisition, rats were separated into four groups to assess drug-substitution and discrimination reversal in Phase 2. The first group maintained the stimulus-reinforcer relation from acquisition (NIC−). The reversal group was now given access to sucrose on nicotine days (NIC+). The substitution group replaced nicotine with varenicline (1 mg/kg) while maintaining the acquisition stimulus-reinforcer relation (VAR−). The substitution and reversal group had nicotine replaced by varenicline and the stimulus-reinforcer relation reversed (VAR+). Rats in all groups learned or maintained their Phase 1 discriminations. For Phase 2, the reversal groups (+ conditions) acquired their discriminations within 10 sessions. The VAR−group displayed a pattern of disrupted discrimination at the outset of Phase 2 but was reestablished after continued training. In substitution testing, VAR groups received nicotine and NIC groups received varenicline. The NIC−and VAR−groups displayed full substitution of the test stimulus whereas the NIC+ and VAR+ groups displayed partial substitution of the test stimulus. Rats underwent nicotine extinction in Phase 3. Initial responding for each group mimicked Phase 2 training (i.e., higher responding by the reversal groups). All rats maintained similarly low levels of responding after six sessions. In conclusion, initial learning history with nicotine (i.e., + or −) influenced drug-stimulus substitution and the rate at which new learning (e.g., reversal) occurs with the varenicline and nicotine interoceptive stimuli